1. Field of the Invention
The present invention relates to an automatic focus detecting apparatus of a lens interchangeable type camera and, more specifically, to an improvement of the automatic focus detecting apparatus when an auxiliary light is employed.
2. Description of the Related Art
Conventionally, in an automatic focus adjusting apparatus in which an auxiliary light is emitted to illuminate an object of low brightness to adjust the focus of a photographic lens using the light reflected therefrom, an idea of driving the photographic lens to a predetermined focusing position before the emission of the auxiliary light has been proposed (see Japanese Patent Laying-Open Gazette No. 136720/1984). Since the reach of the auxiliary light is limited, the range of focus detection becomes smaller compared with a case in which the auxiliary light is not used. Therefore, the initial position of the lens differs dependent on whether the auxiliary light is used or not.
However, in the prior art, no idea has been disclosed in association with the setting of the lens position when the auxiliary light is used and when not.
The auxiliary light emitting apparatus for focus detection normally comprises a light emitting diode and an optical system for projecting light externally attached above the photographic lens or provided on a front surface of the camera body. The focus detecting apparatus provided in the camera body normally comprises a TTL type focus detecting optical system, whose optical axis coinciding with the optical axis of the photographic lens. Therefore, the flux of the optical system for emitting auxiliary light and the flux for focus detection have a parallax, so that the flux for focus detection is completely included in the flux of the optical system for emitting the auxiliary light beyond a prescribed distance (changes dependent on an angle of view) in front of the photographic lens. The focus detection using the auxiliary light cannot be carried out on an object placed nearer. Additionally, if a lens having long focal length is i.e., a tele-photo lens attached to the camera, the auxiliary light is eclipsed by the lens barrel of the lens, so that the object is not illuminated enough by the auxiliary light, preventing the focus detection by means of the auxiliary light. In such cases, the emission of the auxiliary light or setting of the lens at the initial position suitable for focus detection with the auxiliary light is useless, and it may increase the power consumption.